An inductive Boost DC-DC converter is generally used in a low power electronic circuit to provide an output voltage greater than the input voltage. However, a conversion is not possible if the input voltage is very low unless an input transformer is used, which is expensive and significantly complicates the production of such a DC-DC converter. With any state of the art DC-DC converter, it is therefore not possible to envisage an uncomplicated way of providing a sufficient output voltage to power the electronic components of a circuit based on a very low voltage and power from a voltage source.
For a conventional Boost DC-DC converter, the input voltage must generally be higher than 0.6 V in order to provide a sufficient output voltage. Such a DC-DC converter may include an inductor connected to the drains of a PMOS transistor and of an NMOS transistor, which act as switches. The PMOS and NMOS transistors are connected in series between the converter output terminal and the earth terminal. Inductor L is disposed between a positive terminal of the continuous voltage source, and a connection node of the drain terminals of the two transistors of the converter. The source terminal of the NMOS transistor is connected to an earth terminal, while the source terminal of the PMOS transistor is connected to an output terminal supplying the output voltage.
The PMOS and NMOS transistors are operated alternately by a respective control signal across their respective gate terminal. The NMOS transistor is first of all made conductive to linearly increase a current in the inductor in a first phase, while the PMOS transistor is made conductive in a second phase following the first phase to decrease the current in the inductor towards the converter output, to a zero value, and thus to supply a continuous output voltage.
The conventional DC-DC converter includes components such as current sources or comparators or amplifiers requiring a supply voltage of at least 0.6 V for operation. This type of converter is not able to start and operate with a very low input voltage, which could also be used to directly power the components of the converter, which is a drawback.
The article entitled “Energy Harvesters and Energy Processing Circuits” by Yogesh Ramadass of Texas Instruments in Tutorial T3, 2013 dated 17 Feb. 2013, Institute of Electrical and Electronics Engineers of the University of Pennsylvania ISSCC, may be cited in this regard. This article describes, at pages 61 to 68, a type of ultra-low voltage cold start DC-DC converter. The converter can be powered directly by the input voltage supplied by a continuous voltage source. However, the input impedance is not controlled in the converter to allow start-up at a lower voltage, particularly when the input voltage drops, which is a drawback. Further, it does not provide for a very low power start-up, which is a drawback.